package 笔试;

public class 不同的子序列 {
    /**
     *     "" r a b b i t
     * ""  1  0 0 0 0 0 0
     *  r  1  1 0 0 0 0 0
     *  a  1  1 1 0 0 0 0
     *  b  1  1 1 1 0 0 0
     *  b  1  1 1 2 1 0 0
     *  b  1  1 1 3 3 0 0
     *  i  1
     *  t  1
     */

    public int numDistinct(String s, String t) {
        int m = s.length();
        int n = t.length();
        int[][] dp = new int[m+1][n+1];
        for(int i = 0; i < m; i++) {
            dp[i][0] = 1;
        }
        for(int i = 1; i <= m; i++) {
            for(int j = 1; j <= n; j++) {
                if(s.charAt(i-1) == t.charAt(j-1)) {
                    dp[i][j] = dp[i-1][j-1] + dp[i-1][j];
                } else {
                    dp[i][j] = dp[i-1][j];
                }
            }
        }
        return dp[m][n];
    }
}
